Matter-field interaction in atomic physics and quantum optics

Abstract
Almost forty years ago one of us (W.E.L.) noticed that within the analysis of experiments on the hydrogen fine structure the matter-field interaction was sensitive to the choice of gauge when decaying states were used. In the present paper this problem is resolved for the Bethe-Lamb equations in the context of the two-level model with Weisskopf-Wigner decay included.